docs: def main(symbol: str):
      """
  	Displays the balance for the security symbol.
  	"""
      print("Displaying the balance for", symbol)
  
      with BookAggregate() as svc:
          security = svc.book.get(Commodity, mnemonic=symbol)
  		#security.transactions, security.prices
  
          sec_svc = SecurityAggregate(svc.book, security)
  
          # Display number of shares
          shares_no = sec_svc.get_quantity()
          print("Quantity:", shares_no)
  
          # Calculate average price.
          avg_price = sec_svc.get_avg_price()
          print("Average price:", avg_price)